Admixtures of Concrete (Concrete Technology)

Concrete admixtures are chemicals or minerals that modify the properties of concrete. Concrete admixtures have a very wide range of applications and they come under various brand names. The most commonly used admixtures are listed and explained below.

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Plasticizers and Superplasticizers

Plasticizers are used to improve workability while keeping the water-cement ratio constant or in other words, plasticizers improve workability without increasing the water-cement ratio. They are also called water reducers.
The most commonly used plasticizer is Styrene Butadiene Rubber (SBR).
Superplasticizers are high-range water reducers. They are more advanced than plasticizers.
Here are some important types of superplasticizers.

Polycarboxylate ester
Modified lignosulphonates
Cross-linked acrylic polymer

Set Retarders

These are used to reduce the rate of hydration of cement. Set retarders are most commonly used with Ready Mix Concrete. Common sugar is one of the most commonly used Set Retarder. Other admixtures used as Set Retarder are Ligno-sulphonic acids and their salts.

Set Accelerators

Set Accelerators are used to increase the rate of hydration of cement. They have a very wide range of applications as explained below.

It permits earlier removal of formwork.
Reduce the required period of curing.
Advance the time that a structure can be placed in service.
Set accelerators are highly used in emergency repair work.

The most commonly used material, as set accelerators, till the 20th century, was Calcium Chloride, but now with advancements in technology, its use has become obsolete.
Some soluble carbonates are used as set accelerators.

Air-Entraining Admixtures

One of the most important evolutions in concrete technology is the invention of air entraining admixtures. There are two types of air voids in the concrete.

Entrapped air (not a desirable one)
Entrained air It is minute spherical bubbles introduced intentionally ranging in size from 5 microns to 80 microns

Air-Entraining Agents

The following types of Air-Entraining agents are used in today’s age

Natural wood resins
Animal and vegetable fats and oils
Water soluble soaps of resin acids
Aluminium Powder

The major alteration, air entraining admixtures made to the properties of concrete are-

Reduction of strength
Improved workability
Very high resistance to frost action

Pozzolanic Or Mineral Admixtures

These are mainly used to improve durability and decrease permeability. Silica fume, Fly ash, Rice husk ash, Surkhi, and blast furnace slag are commonly used pozzolanic admixtures.
They directly do not contribute to strength but affect permeability.
Other interesting facts about pozzolanic admixtures are-

They reduce the alkali-aggregate reaction
Lower costs of concrete for the same strength
Reduces the Alkali Aggregate reaction

Top 10 Concrete Admixture Companies in India

Fosroc Chemicals India Pvt. Ltd.
Sika India Pvt. Ltd.
Pidilite Industries Ltd.
Chembond Chemicals Ltd.
BASF India Ltd.
Maple Adhesive Industries India Pvt. Ltd.
Fairmate Chemicals Pvt. Ltd.
CICO Technologies Ltd.
Guru Corporation
Krystal Surface Solution